Young children can apply certain emotion words in a manner that is too wide for facial expressions or situations and use other emotion words too narrowly. To explore the extent to which children’s overextension or underextension of emotion words is influenced by mothers’ use of those words, the present study analyzed how mothers talk to their 15- to 18-month-old children. Mothers were asked to explain to their children the emotions of a model using particular facial expressions or those of characters in stories. The results indicated that mothers used some emotion words in a manner that was too wide and other emotion words too narrowly. Mothers’ use of emotion words is partly related to children’s application patterns of those words, especially regarding facial expressions. Regarding the use of emotion words for characters in stories, other factors aside from mothers’ use can contribute to children’s semantic domain of emotion.